He attended La Sapienza University in Rome, where he obtained his doctorate in “utroque jure” on November 23rd , 1736.

His career began in the Diocese of Rome, and lead him to the post of vice-legato (vice ambassador) to Bologna, from 1738 to 1740.

In 1744, within 10 days he received all orders: the minor orders on March 15th, an between 19th and 22nd he was ordained sub-deacon and deacon. On March 25th, he was ordained priest. Less than a month later, on April 13th, 1744, he was appointed Titular Archbishop of Laodicea in Phrygia. His episcopal ordination took place in the Basilica of St. Mary of the Angels and Martyrs in Rome, on April 19th , 1744, when the principal celebrant was the same Pope Benedict XIV.

In the next fifteen years, Jerome had important roles as apostolic nuncio: Cologne from April 23rd, 1744, in Switzerland from January 22nd, 1754 and in Spain on November 8th of that year.

He was created “cardinale presbiterio” by Pope Clement XIII in the consistory of September 24th, 1759. On December 15th, 1760, he was awarded the title of St. Balbina. On March 13th, 1775, he opted for the title of Santa Cecilia. However, a month later, on April 3rd , while keeping “in commendam” the title of Santa Cecilia, he was appointed cardinal-bishop of Palestrina.

As a cardinal, he obtained a number of positions in the Roman Curia; from 1761 to 1768 he was papal legate (ambassador) in Bologna, and later in Ferrara. He took part in two conclaves, in 1769, for the election of Pope Clement XIV, and in 1774-1775, which led to the election of Pope Pius VI.

Girolamo died on July 22nd, 1784 in Rome. His remains rest in the basilica of Santa Cecilia in Trastevere.